LSM3261_Lecture 3 --- Stems and Transport

8/3/2019 LSM3261_Lecture 3 --- Stems and Transport

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LSM 3261 Life Form and Function

ems an ranspor


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Lecture 3 Topics

Shoot system

External stem structure in woody twigs

Stem growth types

Herbaceous eudicot and monocot stems

Cork cambium

Vascular cambium

Annual rings Heartwood and sapwood

Hardwood and softwood

Pathway of water movement

Movement of water in the plant ens on-co es on mo e Root pressure

Pathway of sugar solution movement Pressure-flow hypothesis

Stem modifications


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Reference

Solomon, E.P., L.R. Bergand D.W. Martin. 2011.

Biology. 9th ed.

Cha ter 35


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Shoot System (Revision)

The shoot system componentsinclude:

1. Essential components (primary organs)

a. Stem

b. Leaf

2. Other components (= combination of stem

and modified/unmodified leaves)

a. Axillary bud which can develop into a:

(1) Vegetative branch

(2) Reproductive branch (flower,

n orescence

b. Terminal bud which can develop into a:

(1) Vegetative shoot(2) Reproductive shoot (flower,

inflorescence)


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External Stem Structure in Woody Twigs

Buds (undevelopedembryonic shoots)

erm na u a p o s em

Axillary buds (lateral buds) in leafaxils

Dormant bud covered and protectedy u sca es w c eave u sca e

scars

Node is area on a stem

Internode is regionbetween two successiveno es

Leaf scar remains whenleaf is detached from stem

Bundle scars*

Lenticels*


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Bundle scars arew

scar where vascular

tissue is extended


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Figure 33-8Lenticel

Page 640Lenticel = Porous swellings of corkcells in the stems of woody plants;

cells

Corkcam um

and cork

parenchyma


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Di ression: Co in with Technical Jar on

Every field of human knowledge has jargon

No shortcut to hard work (10,000-hour rule)

in the main texts glossary (if absent in

,

Learn to pronounce the word properly

e.g., vascu ar asc cu ar

Revise regularly For those hard to remember terms, determine

e.g., axil derived from Latin axilla, armpit


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Stem Growth Types

Apical meristems (tip of main stem, tip of

branches)

Lateral meristems (vascular cambium, cork

cambium, other forms [anomalous

secon ary growt ; not covere n t s

module])

Produces primary tissues (epidermis, Produces secondary tissues (secondary

collenchyma, parenchyma, sclerenchyma,

phloem, xylem)

phloem, secondary xylem, cork, cork

parenchyma)

. ., , ,

conifers)

. ., ,

conifers)


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Herbaceous Eudicot and Monocot Stems 1

Similarities Epidermis

Cuticle

Stomata and guard cells

Trichomes

Ground tissue

Collenchyma

Parenc yma c orenc yma

Sclerenchyma

Vascular tissue

Xylem

Phloem

Where would you find the

chlorenchyma?


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Herbaceous Eudicot and Monocot Stems 2a

Eudicot MonocotD erences

Vascular bundles in a ring (with distinct

cortex and pith)

Vascular bundles scattered (without distinct

cortex or pith), or in two or more rings (with

distinct cortex and pith)


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Herbaceous Eudicot and Monocot Stems 2b

Eudicot MonocotD erences

Vascular bundles open (with fascicular

cambium)

Vascular bundles closed (without fascicular

cambium)

Fascicular

Cambium*

*Error on p. 746 of textbook!


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Digression: Fallability of Human Knowledge

Any data source may have errors so you should

be discriminating when reading anything

lies

Reliability of information varies with the source

explicitly


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Woody Eudicots and Gymnosperms

Lateral meristems Cork cambium

Vascular cambium

Anomalous secondar rowth notcovered in this module)

Dracaena sp. stem TS


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Cork Cambium/Phellogen

cambium + cork parenchyma

Cork cambium = phellogen Meristem which produces cork

parenchyma and cork

=phelloderm Phelloderm /cork parenchyma

ce s

Reserve cells for becoming corkcambium when growth shuts

own

For storage in a woody stem

Cork = phellem Cork cells

Replacement for epidermis in awood stem


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Harvested from the corkCork

oak (Quercus suber) Properties of cork

Good insulator for heat or

sound Lightweight

Soft an easy on feet soless tiring to stand on for

Cork tilesor oor ng n a

kitchen

long periods

Cork outer lining of space capsules


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Vascular Cambium 1

Vascular cambium Meristem which produces

secondary phloem

Secondary xylem Transport of water and

mineral nutrients

uppor an e g

For storage

Transport of water and

photosynthates For food storage

Phloem parenchyma cells act

precursors


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Wh do stems have to

become wider to become

a erThe worlds tallest tree is called Hyperion (name from Greek

mythology, one of the Titans, giant Greek gods). It measures

115.6 m (379 ft 4 inches). This coast redwood (Sequoia

sempervirens) was discovered by Chris Atkins and Michael

Taylor (USA) in 25 Aug 2006 in the Redwood National

Park, California, USA.

Aspect ratio = Width Height

Stratospheric Giant, one of the tallest trees in the

World (113.1 m in 2010); formerly the tallest


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Vascular Cambium 2

Interfascicular cambia develop in parenchyma tissuebetween vascular bundles in line with the fascicular

Fascicular cambia and interfascicular cambia connect to

Vascular cambium divides to produce secondary

occasionally divides sideways to produce moremeristematic cells to increase the circumference of the

vascular cambium, necessary because of the growth of

the secondary xylem below

Pr mary xy em an pr mary p oem ecome separate .

Primary xylem gets embedded beneath the secondary

,

the outer tissues of the stem.


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Onset of Secondary Growth


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Beginning of Division of Vascular Cambium


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A Young Woody Stem


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-

ment of

econ ary

X lem andSecondary

=

Secondary

xylem


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Annual Rings a e o grow ce s ze var es w

the season in seasonal climates

growth; cooler and drier conditions

decrease growth Each year of growth shows both cell

types so annual rings form each year

consistin of both:

Early or spring wood (spring when

wetter conditions prevail; larger

cells)

Late or summer wood (late in

prevail; smaller cells)


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Pith Annual rings

Usin AnnualBark Rings for

Dat ng an

Long, slender core of wood

extracted by a boring tool

(basswood)

Outer Vascular

Past Climate

bark Annual rings Pith

Sample from a living tree

cambium

1950

Outermost ring is

the year when the

1940 1932

tree was cut.

in the same forest

1940 1932 1931 1926Sample from an old building

in the same area as the forest

Matching and overlapping olderand older wood sections extends

dates back in time 1931 1926 1920 1918


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Heartwood and Sapwood

Heartwood = Older, dead,darker and heavier wood in

Why call it heartwood?

Heartwood

Vessels and tracheids

plugged up with tannins,gums, res ns, ot er

materials, hence have a

storage function

Sapwood = Younger, livelighter coloured and more

periphery of the trunk

Vessels and tracheids stillfunctioning, hence can

still leak water and

nutrient ions (sap)

Sapwood


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Hardwood and Softwood

Hardwood = Wood ofeudicots

Has vessel elements

and fibres

Softwood = Wood of

conifers

Lacks vessel elementsand fibres; only

tracheids and

parenchyma

Has the de ree of

o r ar ness ca e

Talc: 1 (softest)

Gypsum: 2

Calcite: 3

hardness anything to do

with these types of

Fluorite: 4

Apatite: 5

Feldspar: 6

uartz: 7

wood? Topaz: 8Corundum: 9Diamond: 10 (hardest)


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Balsa (Ochroma pyramidale) Wood

A hardwood which is softer and

more lightweight than most

softwoods!


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Pathway of Water Movement

ater an sso ve nutr ent m nera s move rom sointo

Cortex, etc.

Once in root x lem water and dissolved mineralsmove upward from Root xylem to stem xylem

Stem xylem to leaf xylem

Most water entering leaf exits leaf veins and passes

f i h l


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Movement of Water in the Plant

Tension-cohesion model

Root pressure

T i C h i M d l 1


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Tension-Cohesion Model 1

ater potent a s a measure othe free energy of water

Pure water has a water potential of

0 megapascals

ater w t sso ve so utes as

negative water potential

a er moves rom an area o

higher (less negative) water

po en a o an area o ower

(more negative) water potential

roug a sem -permea e

membrane

T i C h i M d l 2


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Tension-Cohesion Model 2

The tension-cohesion modelexplains the rise of water anddissolved nutrient minerals inxylem

Transpiration causes tension at

Tension at top of plant resultsfrom water potential gradientrang ng

From slightly negative waterpotentials in soil and roots

o very nega ve wa er po en a sin atmosphere

Column of water pulled uproug p an rema ns un ro en

due to properties of water

Cohesive

A es ve

R P


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Root Pressure

Root pressure = The pressure inxylem sap that occurs as a result of

the active absorption of mineral

ions followed by the osmoticupta e o water nto root rom t e

soil

Caused by movement of water into

roots from soil as a result of active

a sorp on o nu r en m nera ons

from soil

e ps exp a n r se o wa er n

smaller plants (especially when

Pushes water up through xylem

h f l i


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Pathway of Sugar Translocation

Dissolved sugar is translocated up or down in phloem

,

To a sink (area of storage or of sugar use)

rea o s orage or o sugar use

Roots

p ca mer stems ( ru ts an see s)

Sucrose is predominant sugar translocated in phloem

Why transport sucrose (disaccharide)

an no g ucose monosacc ar e

which is manufactured by the leaf?


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Aphids used to study translocation in plants

H S S l i I T d


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How Sugar Solution Is Transported

Pressure-flow hypothesis explains the movement of materials in phloem Companion cells actively load sugar into sieve tubes at source ATP required for this process

ATP supplies energy to pump protons out of sieve tube elements

Proton gradient drives uptake of sugar by cotransport of protons back into

sieve tube elements Sugar therefore accumulates in sieve tube element

This causes movement of water into the sieve tubes by osmosis therebyincreasing the turgor pressure

Companion cells unload sugar from sieve tubes at sink Actively (requiring ATP)

Passively (not requiring ATP)

As a result, water leaves sieve tubes by osmosis

Unloading of sugar causes decrease in turgor pressure inside sieve tubes

Flow of materials between source and sink is driven by turgor pressuregradient produced by Water entering phloem at source

Water leaving phloem at sink

Th P Fl H th i


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The Pressure-Flow Hypothesis

(diagram divided in two)

M difi ti f th St


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Modifications of the Stem

1. Bulb

2. Cladode

.

4. Rhizome

. en r

6. Thorn

7. Tuber

Unmodified stem

M difi ti f th St


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Bulb =

Short, erect,

un ergroun stem

surrounded b flesh

leaf bases

Onion llium ce a bulb insection


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Cladode =

A green stem which takes on the function of

p otosynt es s rom t e re uce eaves

(Casuarina

equisetifolia)


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Corm =

An enlarged, solid,

es y ase o a stem

with scale leaves

Coco am Alocasia esculenta and

water chestnut (Elaeocharis

dulcis)


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Rhizome =

A horizontal stem

grow ng on or

under round

Ginger(Zingiber officinale)


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Tendril =

A long, slender,

co ng ranc or

climbin

Corky passionflower (Passiflora suberosa)


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Thorn =

A leafless branch

w t po nte t p

and which

develops from

Bougainvillea (Bougainvillea hybrid)


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Thorns develop from

axillary buds

Spines are associated

Prickles are outgrowths

of the stem epidermis

but not axillary buds

Rose (Rosa cultivar)



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Tuber =

A thick storage stem

Potato Solanum tuberosumunderground

LSM3261_Lecture 3 --- Stems and Transport

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